Known gas laser systems use electrical discharges between DC or AC electrodes within transfer or axial flows. However, utilization of DC or AC electrodes, within fast subsonic and especially supersonic flows, creates unstable and non-uniform plasma discharges. These non-uniform discharges produce aerodynamic instability of the gas flow. This instability, characterized by wave shocks and turbulence, is proportional to the static pressure of the flow and volume in the discharge region between DC or AC electrodes. These limitations prevent creation of a stable, uniform and continuous plasma. In addition, AC/DC discharges create aerodynamic resistance for gas flows which requires a higher power gas pump. The aerodynamic instability of the supersonic and subsonic flows generated in the known gas lasers produce regions of increased temperature, related to the wave shocks, as well as temperature pulsation's, related to the turbulence. These factors are responsible for reduction of the laser inversion population, efficiency of the laser and optical quality of the flow within the resonator region.
Gas medium excitations utilizing glow DC or AC discharges are also well known. These laser designs, however, have other fundamental problems. The ARC plasma regions or those areas exhibiting sparking instability create a high atomic temperature of the laser gas which is therefore free from laser inversion population required for generating lasing activity and causes a breakdown in optical quality. Additionally, such sparking instability can lead to chemical composition breakdown of the gas active medium. Relative to the RF glow discharges, DC or AC glow discharges have a reduced energy contribution to the same volume of stable non-equilibrium plasma. Typically RF density requirement for excitation has a range from 10 to 100 watt per cubic cm., depending on RF frequency and type of RF plasma (Alpha or Gamma). In the case of DC and AC glow discharges for identical gas conditions the range of maximum possible densities is only from 1 to 5 watt per cub. cm. above which the sparking-plasma instability has taken place.
There is also a principle difference between natures of RF and DC/AC plasma structures. DC or AC discharges are based on the direct current of electrons and ions between an anode and a cathode. RF or High Frequency Discharge excitation is based on the high frequency oscillation of electron's boundaries located on the RF electrodes and stimulation of a "Positive Column" of ions and negative electrons between RF electrodes with the help of high frequency ionization by collision mechanisms. This means that DC and AC discharges are much more capable of the disintegration of chemical stability of the laser gas medium based on the dissociation, for example, of CO.sub.2 molecules to molecules of CO and atoms of O. That is why RF discharges are superior to DC/AC type of discharges in the following respects: chemical stability of the laser gas; energy contribution to the volume of plasma; optical quality of the active medium; and level of power of gas pump required for providing gas medium flow.